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Hayabusa

The issue of the journal Science from 26 August 2011 vol 333 pp 1113-1131 has six articles on the Hayabusa sample return mission from the asteroid Itokawa. The first article is discussed here, the second here, and this is the third:

Neutron Activation Analysis of a Particle from Asteroid Itokawa

A single grain from the Hayabusa mission has been analyzed by instrumental neutron activation analysis (INAA). The grain was mainly olivine, with minor amounts of plagioclase, troilite and metal.

This grain was one of the largest returned by the Hayabusa mission. The scanning electron microprobe (SEM) results show this to be a large crystal of olivine. Small pieces of silicate were attached to the surface. Radioactive analysis indicates that the grain is relatively homogeneous.

Comparison of the INAA analysis of this grain from Itokawa with from an LL6 chondrite (St Severin) and an L6 chondrite (Modoc) indicated an elemental abundance discrepancy.

Iron (Fe) and Scandium (Sc) abundance can be determined reliably, and the ratio is determined by the differentiation of iron into the core of a body during its formation. In particular, the Fe/Sc ratios from the Earth, Moon, Mars and 4Vesta are lower than those of chondrites. The ratios from Itokawa are higher than those from terrestrial olivine, and are thus from an extraterrestrial origin. This increases confidence that Hayabusa did return samples from Itokawa.

Nickel (Ni) and Cobalt (Co) typically diffuse into a metal phase. The ratio of Ni/Co in bulk chondrites plot along a line with carbonaceous chondrites. Samples from the Earth’s crust are relatively depleted in Nickel compared to Cobalt, and thus are distinguished from the grain returned from Itokawa.

In addition, Iridium (Ir) abundances were estimated, and the result indicates that the sample must have condensed from a fractionated nebula gas where refractory siderophiles such as Iridium had already condensed and been removed.

The issue of the journal Science from 26 August 2011 vol 333 pp 1113-1131 has six articles on the Hayabusa sample return mission from the asteroid Itokawa. The first article is discussed here, and this is the second:

Oxygen Isotopic Compositions of Asteroidal Materials Returned from Itokawa

Minerals within bodies of the Solar System have unique oxygen isotope ratios, thought to be determined by gas-dust chemistry and accretion physics. However, the Earth and the Moon are the only bodies for which isotope ratios are known.

Twenty-eight (28) of the sample grains returned by Hayabusa were analyzed for oxygen isotope abundances. The ratios were compared to the ordinary chondrite meteorite Ensisheim (an LL-6 chondrite) and Earth minerals, and the uncertainty in measurements were calibrated against standard mean ocean water (SMOW) from Earth. The results show that the grains returned by Hayabusa are not of terrestrial origin. One of the Earth minerals was a fosterite crystal from San Carlos, Arizona.

Chondrites are classed as H, L or LL, and the samples from Itokawa are clearly L or LL and not H. The variation in ratios between samples indicates the degree of equilibration due to metamorphic heating. These data indicate that the samples from Itokawa experienced temperatures between 600 C and 720 C, which is lower than LL6 chondrites and higher than LL4 chondrites.

These results are consistent with those from those reported in the first paper and provide unequivocal evidence that ordinary chondrites come from S-Type asteroids.

The results are from the first samples retrieved from the sample catcher. A Teflon spatula successfully swept about 10% of the sample catcher’s surface. 1534 particles have been identified with the field-emission scanning electron microscope. There were 1087 mono-mineral grains:

580 olivine particles

126 low Calcium pyroxenes

56 high Calcium pyroxenes

186 feldspars

113 troilites

13 chromites

10 Calcium phosphates

3 Iron-Nickel grains

The remaining 447 particles bear several minerals, mostly silicates.

The sample catcher was also “tapped” to retrieve additional particles. 38 of these particles have been closely examined. Six are poorly differentiated and 32 are highly differentiated. The 32 highly differentiated particles indicate they have undergone intense thermal metamorphism. There is almost complete partitioning of the Magnesium, Iron and Calcium between pyroxenes. Ordinary chondrite meteorites exhibit thermal metamorphism ranging from unequilibrated type 3 to completely equilibrated type 6. Measurements indicate that the particles formed at a peak temperature of 800 C and cooled slowly to 600 C. The slow cooling indicates that the particles from Itokawa formed at considerable depth. This suggests that the parent body was destroyed by one or more catastrophic impacts. Remnants reformed into present day rubble pile asteroids, including Itokawa.

Petrologic data from the study shows that Itokawa is an ordinary chondrite, linking these asteroids with the corresponding meteorites.

The new issue of Science (15 April 2011 vol 232 p 302) discusses the current status of analyses of the samples returned from the asteroid Itokawa. It is a solid scientific success. The results were presented by Japanese scientists at the Lunar and Planetary Science Conference in The Woodlands, Texas, from 7 – 11 March 2011.

Analysis has confirmed that the S-type class of asteroids covered by a mysterious discoloration is the source of the most common meteorite that falls to Earth. Decades ago, research had suggested the composition of these asteroids was different from chondrite meteorites.

However, by 2001, Richard Binzel and others at MIT had concluded from telescopic observations that Itokawa belongs to the distinctive LL subclass of ordinary chondritic asteroids that had been “weathered” by exposure to space.

The first task was to remove any particles from the collection mechanism, which had malfunctioned in spectacular fashion. A specially designed extraction tool was a failure. A Teflon spatula was a bit better, but the best result came from striking the overturned canister with a screwdriver. 20 sharp raps did the trick. About 1500 particles from Itokawa were recovered. All smaller than 100 micrometers.

Researchers across Japan took 52 of these particles and applied a range of microanalytical techniques – XRD, XRF, UMT, FIB, TEM, SEM, EPMA and SIMS. This alphabet soup clearly showed that Itokawa was a space-weathered ordinary LL chondrite asteroid. A great win for Hayabusa.

Additional research is now underway to determine what sort of space weathering is involved in producing the discoloration.

Previous NSS Phoenix blog entries about the intrepid Hayabusa can be found at:

That is the headline on this week’s Aviation Week and Space Technology’s article on the preliminary results from the compartment containing samples from the second landing on the asteroid Itokawa. The Hayabusa team has cataloged the particles found inside and determined that the majority are primitive minerals, and that they differ from Earth’s surface rocks.

Scanning Electron Microscope (SEM) revealed approximately 1500 grains that appear to be rocky material and most are of extraterrestrial origin. Comparison of these grains with samples from the Earth show that they differ from Earth rocks. Remote sensing data collected by the X-Ray Fluorescent Spectrometer (XRS) and the Near-Infrared Spectrometer (NIRS) on the Hayabusa spacecraft during the encounter with Itokawa support the results from the sample return compartment.

The grains are on average less than 10 micrometers in size, and include olivine, pyroxene, iron sulfide and plagioclase.

JAXA is developing the necessary handling techniques and preparing the associated equipment for the initial (but more detailed) analyses of these ultra-minute particles.

The sample compartment from the first landing has not been opened, and may well contain more particles than those recovered from the first compartment.

At NSS Phoenix, we have been noticed by the space faring community in Korea. Although the translation by Google is perhaps notional rather than idiomatic, nevertheless, we share the sentiments. The quote below references “The Little Spacecraft That Could“.

Hayabusa arc while returning to Earth has been battered. Burned body, while the plunge into Earth’s atmosphere, prior to separating the capsule placed on the landing area was the only Australian woomera.

Pretty nice chronicle the related description that I saw the translation, and in addition introduced here is moderation. The original sources are listed below.

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David Brandt-Erichsen

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